Background noise is often superposed on a voice signal inputted from a microphone or a hand set or the like, and it becomes a big problem when voice coding and voice recognition are performed. As a signal processing device which aimed at cancellation of acoustically superposed noise, a 2-input type noise cancellation device using an adaptive filter is disclosed by patent document 1.
The 2-input type noise cancellation device disclosed by patent document 1 uses the adaptive filter which approximates impulse response in a acoustic path (a noise path) from a noise source to the voice input terminal to generate pseudo-noise corresponding to noise components which are mixed in voice at the voice input terminal. And, by subtracting the pseudo-noise from a signal (a mixed signal) inputted to the voice input terminal, the noise cancellation device operates so that the noise components may be suppressed. Here, the mixed signal means a signal in which a voice signal and noise are mixed, and generally supplied from a microphone or a hand set to the voice input terminal. Further, a reference signal means a signal which has a correlation with the noise components in the noise source, and captured in the vicinity of the noise source. In this way, by capturing the reference signal in the vicinity of the noise source, it is possible to assume that the reference signal is approximately equal to the noise components in the noise source. To the adaptive filter, the reference signal supplied to a reference input terminal is inputted.